There is conventionally a memory system including a non-volatile memory, a volatile memory, and a rechargeable battery. Various pieces of data are cached in the volatile memory. In a normal power off sequence, the various pieces of data cached in the volatile memory are written into the non-volatile memory using power supplied from the outside. When power-down different from normal occurs, energy stored in the rechargeable battery is used to write the various pieces of data into the non-volatile memory.